Short: we use a Django frontend to an Erlang backend. Long answer: we used Django because that's what I knew best, but we're going to switch to Pylons because

Short: we use a Django frontend to an Erlang backend. Long answer: we used Django because that's what I knew best, but we're going to switch to Pylons because it's more flexible (being a so-called "glue framework") and has less dependency on a database (tried writing a custom authentication backend in Django without a database? Good luck). So Django is great if you have a database; less so if you don't (I guess that's the whole "full stack" thing).